Acrylamide has been conventionally produced industrially by hydrating acrylonitrile corresponding thereto using copper in the reduced state as a catalyst. Recently, a method using a microbial catalyst instead of a copper catalyst has been developed, and a part of this method is in actual use. A biocatalytic method using a microbial catalyst or the like has promise as an industrial production method, because the method has moderate reaction conditions and yields almost no by-product, so that an extremely simple process can be designed for this method. Thus, many microorganisms having an enzyme (enzyme name: nitrilehydratase) capable of catalyzing (converting) acrylonitrile into acrylamide by hydration have been found so far.
Examples of these microorganisms include microbial strains belonging to the genera Bacillus, Bacteridium, Micrococcus, Brevibacterium [see JP Patent Publication (Kokoku) No. 62-21519 B (1987) for the above microorganisms], Corynebacterium and Nocardia [see JP Patent Publication (Kokoku) No. 56-17918 B (1981) for the above microorganisms], Pseudomonas [see JP Patent Publication (Kokoku) No. 59-37951 B (1984)], Rhodococcus and Microbacterium [see JP Patent Publication (Kokoku) No. 4-4873 B (1992) for the above microorganisms], Rhodococcus rhodochrous [see JP Patent Publication (Kokoku) No. 6-55148 B (1994)], and Rhodococcus [see JP Patent Publication (Kokoku) No. 7-40948 B (1995)].
Examples of a process for producing acrylamide using the above microorganism as a microbial catalyst include those of JP Patent Publication (Kokai) Nos. 11-123098 A (1999) and 7-265091 A (1995), and JP Patent Publication (Kokoku) No. 56-38118 B (1981). An example of the reaction method is that of JP Patent Publication (Kokai) No. 11-89575 A (1999).
Further, a variety of studies have been conducted for improving enzyme activity or suppressing a decrease (deactivation of) in enzyme activity during reaction. Examples of such a study include a process which involves performing reaction at a low temperature, 15° C. below freezing point [see JP Patent Publication (Kokoku) No. 56-38118 B (1981)], a process which involves sequentially supplying a substrate at a low concentration from multiple supply openings [see JP Patent Publication (Kokoku) No. 57-1234 B (1982)], a process which involves treating microorganisms or the treated product thereof with an organic solvent [see JP Patent Publication (Kokai) No. 5-308980 A (1993)] a process which involves performing reaction under the presence of higher unsaturated fatty acid [see JP Patent Publication (Kokai) No. 7-265090 A (1995)], and a process which involves subjecting microbial cells to cross-linking treatment with glutaraldehyde or the like [see JP Patent Publication (Kokai) Nos. 7-265091 A (1995) and 8-154691 A (1996)].
In the meantime, for washing a microbial catalyst, the generally known methods involve washing using a physiological saline, a buffer such as an aqueous solution of phosphate or Tris hydrochroride to suppress a decrease in enzyme activity. However, there is no report on the washing of a microbial catalyst wherein the effects of wash components on the physical properties of acrylamide polymers and the storage stability of monomers have been considered.
As described above, a process for producing acrylamide using a microbial catalyst has promise as an industrial production process, because the process employs moderate reaction conditions and yields almost no by-product, so that no purification is required and an extremely simple process may be designed.
Although the above production processes yield no by-product upon enzyme reaction, they have a drawback such that when a microbial catalyst to be used is washed, contamination of impurities derived from the wash affects the physical properties of acrylamide polymers and the storage stability of acrylamide monomers. To address the problem, purification such as crystallization, ion exchange, or distillation can be performed. With these purification processes, however, an outstanding characteristic of a production process using a microbial catalyst, that is, to yield almost no by-product upon reaction, cannot be utilized. Moreover, the use of these processes is also unfavorable in terms of energy and environmental problems.